1. Field of the Invention
The present invention relates to a liquid droplet discharge head and an image forming apparatus, and more particularly, to a structure of a liquid droplet discharge head which discharges liquid droplets from nozzles by applying pressure to liquid by driving actuators, and an inkjet recording apparatus or other image forming apparatus using a liquid droplet discharge head of this kind.
2. Description of the Related Art
Japanese Patent Application Publication No. 60-115457 discloses an inkjet head having a structure in which the minute vibrational displacement of a piezoelectric diaphragm is transmitted to a passive diaphragm of small surface area by means of a horn-shaped displacement amplifying chamber, thereby causing ink inside an ink chamber which is positioned in front of the passive diaphragm to be discharged from an orifice (liquid droplet discharge port).
Japanese Patent Application Publication No. 2000-43267 discloses an inkjet head comprising two pressure generating chambers for each nozzle, in order to increase the speed of ink refilling to the pressure generating chambers after ink discharge. This head is provided with a first pressure generating chamber and a second pressure generating chamber connected to a common ink chamber (reservoir), these two pressure generating chambers being connected mutually as well as being connected to the same nozzle, by means of a nozzle connection hole. A second ink supply port which connects the second pressure generating chamber with the reservoir is positioned nearer to the nozzle opening than the first ink supply port which connects the first pressure generating chamber with the reservoir. In this way, a structure is achieved in which, after an ink droplet has been discharged due to deformation of the piezoelectric element, ink flows into the first pressure generating chamber from a flow path of low flow resistance which passes through the second ink supply port of the second pressure chamber generating chamber.
Furthermore, Japanese Patent Application Publication No. 2001-260347 proposes a composition in which pressure chambers corresponding to nozzles are layered in a tiered structure inside a head, in order to achieve high nozzle density for realizing high-resolution printing.
However, Japanese Patent Application Publication No. 60-115457 has a structure based on a horn shape which causes the traveling ultrasonic wave to converge gradually, and therefore, the displacement amplifying chambers must be of uniform size in all three dimensional directions. This makes it difficult to achieve a high level of integration (high density).
The technology disclosed in Japanese Patent Application Publication No. 2000-43267 provides a complementary flow path (second pressure generating chamber) in the vicinity of each nozzle, in order to increase refilling speed. However, since the individual flow paths from the reservoir to each nozzle cannot actually be shortened, the effect of this structure is limited to improving performance in terms of faster refilling speed.
Japanese Patent Application Publication No. 2001-260347 makes it possible to achieve high nozzle density, but since the distance (flow path length) to the respective nozzle openings from the first and second pressure chambers disposed in a tiered fashion differs between the upper and lower tiers, a problem arises in that the discharge characteristics are different for each tier. In order to achieve uniform discharge characteristics in the upper and lower pressure chambers, it is necessary to design the flow channels individually, or to modify the drive control method accordingly. However, taking into account factors such as assembly precision, temperature characteristics, air bubble accumulation characteristics, and the like, it is extremely difficult to achieve uniform characteristics in the respective pressure chambers.